As a light source to be used for a projection display unit such as a projector, a solid-state light source having a long operating life and a wide color gamut has drawn the attention. In recent years, a light source device that utilizes light emitted from a fluorescent body by irradiation of the fluorescent body with light from the solid-state light source has been made available for the projector or any other equivalent display apparatus.
The above-described light source device includes, for example, a fluorescent layer, and a solid-state light source that irradiates the fluorescent layer with excitation light. A phenomenon called luminance saturation or temperature quenching is present in light emission of the fluorescent layer. This is the phenomenon in which a portion of conversion loss in the fluorescent layer is changed into heat to cause the fluorescent layer to produce heat in a case where an output of the excitation light is raised, resulting in deterioration in the fluorescence conversion efficiency. In a state of the low fluorescence conversion efficiency, it is not possible to achieve a bright and efficient light source device. Therefore, the fluorescent layer is provided on a surface of a substrate having high thermal conductivity.